ahh I see, FWIW I sometimes wonder what sentience really is..... and can be forms of intelligence other than biological? Consider the fossilized record of the planet a form of "memory". Perhaps in our search for ET we have to consider entities that are not biological. Not hunks of rocks per se, but things we would never consider as being "alive." Because by many definitions, something like fire can even be considered alive.
I believe that the planet maintains ecological balance at any cost because that's the first law of thermodynamics and also because if it didn't life would have ceased to exist long ago. About the Gaia vs humanity thing, that cant be true either, because human beings are part of the system not against it. Mass extinctions being cases in point, have you noted how evolution explodes after a mass extinction event? The series on PBS/Nature showing how mammals started to evolve rapidly a scant 300,000 years after the Cretaceous mass extinction is a case in point. But nothing exists forever. The humanity caused mass extinction may lead to such an explosion in evolution, or it might destroy all life on the planet forever. It's too early to say which. Those of us who aren't tainted by greed and want sustainable renewables to become the new norm fight for the existence of the entire planet, but humanity's own short-sighted nature gets in the way. I do see a turning point though, where many many more voices have risen up against the status quo and perhaps a difference has been made there that will counteract all the dark money lined up against us.